1. Technical Field
The present invention relates to a conductive composition that contains a π-conjugated conductive polymer and that is dispersible and soluble in a solvent, a production method thereof, an antistatic resin composition obtained by mixing the conductive composition with a resin component, and an antistatic resin film obtained by curing the antistatic resin composition.
2. Related Art
A π-conjugated conductive polymer whose main chain includes a conjugated system containing π electrons is generally synthesized by an electropolymerization method or a chemical oxidative polymerization method. In the electropolymerization method, a mixed solution of an electrolyte serving as a dopant and a precursor monomer for formation of a π-conjugated conductive polymer is prepared, electrodes are placed in the solution and also a support such as an electrode material formed in advance is immersed therein, and a voltage is applied between the electrodes to thereby form a π-conjugated conductive polymer in the form of a film on the surface of the support. The electropolymerization method is thus needed to use an apparatus for electropolymerization and is performed by batch production, and therefore is poor in mass productivity. On the other hand, in the chemical oxidative polymerization method, there are no such limitations as described above, and an oxidant and an oxidative polymerization catalyst can be added to a precursor monomer for formation of a π-conjugated conductive polymer, to thereby produce a large amount of a π-conjugated conductive polymer in a solution.
In the chemical oxidative polymerization method, however, as the conjugated system of the main chain forming the π-conjugated conductive polymer is grown, the π-conjugated conductive polymer is poorer in solubility in a solvent, and therefore is obtained in the form of a solid powder that is insoluble in a solvent. Therefore, it is difficult to form a film of the π-conjugated conductive polymer, having a uniform thickness, on various substrates such as a plastic substrate by a procedure such as coating. There have been attempted based on such reasons a method of introducing a functional group to the π-conjugated conductive polymer to allow the polymer to be solubilized in a solvent, a method of dispersing the π-conjugated conductive polymer in a binder resin to allow the polymer to be solubilized in a solvent, a method of adding an anion group-containing polymeric acid to the π-conjugated conductive polymer to allow the polymer to be solubilized in a solvent, and the like.
For example, in order to enhance the solubility of the π-conjugated conductive polymer in water, there is known a method of subjecting 3,4-dialkoxythiophene to chemical oxidative polymerization using an oxidant in the presence of polystyrenesulfonic acid having a molecular weight of 2,000 to 500,000 as the anion group-containing polymeric acid, to produce an aqueous poly(3,4-dialkoxythiophene) solution (see, for example, Patent Literature 1). There is also known a method of subjecting a precursor monomer for formation of the π-conjugated conductive polymer to chemical oxidative polymerization in the presence of polyacrylic acid, to produce an aqueous colloidal π-conjugated conductive polymer solution (see, for example, Patent Literature 2).
Furthermore, there is also proposed a method of producing a conductive solution that can be solubilized or dispersed in an organic solvent to be mixed with an organic resin. As one example thereof, there are known a solution of polyaniline in an organic solvent, and a production method thereof (see, for example, Patent Literature 3). There is also known a solvent replacement method by phase transition from a solution containing a polyanion and a true conductive polymer in water to an organic solvent (see, for example, Patent Literature 4, Patent Literature 5, Patent Literature 6 and Patent Literature 7). There is also known a method of dissolving a freeze-dried true conductive polymer in an organic solvent (see, for example, Patent Literature 8). These methods, however, have the problem of mixing with other organic resin as in the example of polyaniline, and additionally the problem of limitation to a solvent system containing a large amount of water. Even when a small amount of water or substantially no water is contained, there is the following problem: an amine compound is used to thereby cause color tone to be deteriorated over time in the case of mixing with the resin, and cause doping of the conductive polymer with the polyanion to be gradually withdrawn by amine, resulting in deterioration in conductivity over time, as in the cases of the above Literatures (see, for example, Patent Literature 4, Patent Literature 5, Patent Literature 6 and Patent Literature 7).
In the case of imparting conductivity to a resin where an isocyanate type compound is used, as a characteristic example, there is the following disadvantage: aggregation of a conductive polymer due to amine occurs. Furthermore, if a conductive polymer is mixed with an addition curing type silicone resin, there is the following disadvantage: curing inhibition due to amine occurs to cause curing of a silicone resin to be insufficient.
As described above, there has been heretofore proposed a conductive polymer solution including a π-conjugated conductive polymer, which is a conductive solution that is an aqueous solution, a part or all of which is displaced with an organic solvent, by the prior arts (techniques disclosed in Patent Literatures 1 to 8).